Introduction to Types of Foundation

Basic Introduction to Types of Foundations

1. SOIL MECHANICS AND FOUNDATION ENGINEERING

“In Pursue of Diploma in Civil Engineering”

Prepared By: Phurba Tamang
Designation: Associate lecturer
Department of Civil Engineering & Surveying
Jigme Namgyel Engineering College
Royal University of Bhutan

2. WHAT IS A FOUNDATION?

The low artificially built part of a structure which transmits the load of the structure to
the ground is called foundation.

OR
A foundation is a structure that transfers the load to the ground.

+ A structure essentially consists of two parts, namely the super structure which is above
the plinth level and the substructure which is below the plinth level.

+ Substructure is otherwise known as the foundation and this forms the base for any
structure. Generally about 30% of the total construction cost is spent on the
foundation.

+» The soil on which the foundation rests is called the “foundation soil”.

3. OBJECTIVES OF A FOUNDATION

A foundation is provided for the following purposes:

+ To distribute the total load coming on the structure on a larger area.

+ To support the structures.

* To give enough stability to the structures against various disturbing
forces, such as wind and rain.

+ To prepare a level surface for concreting and masonry work.

“To ensure that the structural loads are transmitted to the subsoil safely, economically
and without any unacceptable movement during the construction period and
throughout the anticipated life of the building or structure”

5. TYPES OF FOUNDATION

N
Foundation
NY

TT TS

Shallow Foundation Deep Foundation

SS SS
Shallow Foundation: Deep Foundation (if D>W)
a) Isolated Footing a) Pile Foundation

b) Combined Footing

c) Raft/Mat Foundation

d) Wall or strip footing

e) Stepped footing and so on.

6. SHALLOW FOUNDATION

Shallow foundations are constructed where soil layer at shallow depth (up to 1.5 m) is
able to support the structural loads (Depth of foundation is less than or equal to its
width)

i. Isolated Footing

i + In framed structures where several columns are to be
constructed, isolated footings can be adopted.

+ The columns involved can be provided with masonry or
concrete footing.

+ if masonry footing is provided, steps are given and the
foundation area is thus increased so that the stresses
developed at the base is within the limit.

+ Concrete can be molded to any shape and hence a concrete
footing may be a sloping one to provide sufficient spread.

+ Economical when columns are placed at longer distances.

7. ii. Combined Footing

* This type of footing is adopted when the space between two
columns is so small that the foundation for individual columns
will overlap.

* Combined footings are proportioned in such a way that the
center of gravity of the loads coincides with the centre of
gravity of the foundation. Hence these footings have either a
trapezoidal or a rectangular shape.

+ Generally, preferred when the soil is wet (marshy areas) to

reduce the pressure on the ground

“Footings are structural members used to support columns and
walls and to transmit and distribute their loads to the soil in such
a way that the load bearing capacity of the soil is not exceeded.
Also excessive settlement, differential settlement or rotation are
prevented and adequate safety against overturning or sliding is
maintained.”

8. SHALLOW FOUNDATION

iii. Raft or Mat Foundation

+ Used to spread the load of the structure over
a large base to reduce the load per unit area
being imposed on the ground

+ Particularly useful where low bearing capacity
soils are encountered & where individual
column loads are heavy.

+ Used when the subsoil is weak.

9. Used when the soil has good bearing capacity
The width of footing deeps on the structural
load

Transmits the weight of load bearing wall
across the area of the soil

10. DEEP FOUNDATION

The shallow foundations may not be economical or even possible when the soil bearing
capacity near the surface is too low. In those cases deep foundations are used to transfer
loads to a stronger layer, which may be located at a significant depth below the ground
surface.

Pile Foundation

Can be defined as a series of columns constructed or inserted
into the ground to transmit the loads of a structure to a lower
level of subsoil

Can be used when suitable foundation conditions are not
presented at or near ground level.

11. DEEP FOUNDATION

Deep foundation type is of a foundation. Different from shallow foundation by depth
they are embedded into earth. There are some reason for set up deep foundation, they
are low bearing soil conditions, heavy super structure load and height rise structure. There
are variety of foundation available, pile foundations (end bearing pile, friction pile,
tensile pile, sheet piles, soldier type pile and etc), slurry walls

Pile Foundation
Pile foundations are deep foundations.

12. PILE FOUNDATION

Pile Foundation classifications
Piles may be classified by their basic design function (end-bearing, friction or a
combination) or by their method of Installing (replacement (driven) or displacement

(bored)).

13. PILE FOUNDATION CLASSIFICATION BY INSTALLING

Displacement Piles/ Driven Piles

Displacement Piles which are driven are termed ‘Displacement Piles’ because their
installation methods displace laterally the soils through which they are introduced
Installation techniques Dropping weight The dropping weight or drop hammer is the
most commonly used method of insertion of displacement piles

Example:

+ Steel pile, concrete spun piles

+» Precast Concrete Piles, Timber piles

14. PILE FOUNDATION CLASSIFICATION BY INSTALLING

PLACEMENT OF PILE

15. PILE FOUNDATION CLASSIFICATION BY INSTALLING

Replacement Piles / Bored Piles
Replacement Piles that are formed by creating a borehole into which the pile is then cast
or placed, are referred to as ‘Replacement Piles’ because existing material, usually soil is

removed as part of the process.

Examples: Bored Piles

16. PILE FOUNDATION CLASSIFICATION BY INSTALLING

Phase 1 Phase 2 Phase 3 Phase 4 Phase 5
Casing installation Drilling Install reinforcement Pour concrete Extract the casing

17. These piles
transfer their
load on to a
firm stratum
like rock.
Installed when
soil bearing

capacity is low.

Pre fabricated
files and auger
type pile can
be used.

End Bearing Pile Friction Pile

q

Strong Soil
or Rock

Friction piles
carry the
major part of
Inads only by
means of
friction
developed
between pile
shaft and soil.

19. DEEP FOUNDATION

Structure
1483 ft (452m)

Foundation
394 ft (120m)

20. DEEP FOUNDATION

21. FUNCTIONS OF FOUNDATION

Distribution of loads
Stability against sliding & overturning

Minimize differential settlement

Safe against undermining

Provide level surface

Minimize distress against soil movement

22. BASIC DESIGN PROCEDURE

Calculation of anticipated structural
loading

.
Assessment of site conditions in
the context of the site & soil
investigation report

Sizing the chosen
foundation in the
context of loading,

ground bearing
capacity & any likely
future movement of

O the building /
structure

Choosing the foundation type, should consider:

1. Soil condition.

2. Type of structure.

3, Structural loading.

4. Economic factors.

5. Time factor relative to the proposed contract
period.

6. Construction problem.

23. FOUNDATION FAILU

24. THANK YOU

PHURBA TAMANG
% JIMGE NAMGYEL ENGINEERING COLLEGE

DEPARTMENT OF CIVIL ENGINEERING AND SURVEYING
DEWATHANG, BHUTAN

a [email protected]
Ÿ 17955951